Electric motor



Feb. 19, 1935. G, Z'EININGER 1,992,131

ELECTRIC MOTOR Filed April 18, 1952 Patented F eb. 19, 1935 UNITED STATES Emormc MOTOR Gustav Zeininger, Oberessiingen, Germany, as-

signor to Robert Bosch Aktiengcscllschait,

Stuttgart, Germany Application April 18, 1932, Serial No. 606,018

In Germany 3 Claims.

The present invention relates to electrical motors and more particularly to small tri-polar armature motors.

Small electrical machines having a tri-polar '5 armature are employed, more especially for operating wipers for the windscreens of vehicles. In certain positions of the armature the turningmoment is at a minimum, so that more particularly in an unfavourable position of the gearing coupled with the armature the motor cannot start; This drawback is avoided according to the invention by attraction edges being formed on the armature or field core by grooves, prongs and the like, which cause a distribution of the magnetic fiux which increases the. turning moment, so that the turning moment in the region of its minimum is improved as compared with the value attainable by the construction hitherto usual.

In the drawing, diagrammatic illustrations of three examples of construction of the invention are illustrated, in which:-

Figure 1 shows one construction,

c Figure 2 a second construction.

Figure 3 a third construction, and

Figure 4 a section through awindscreen wiper motor according to Figure l.

Figure 1 shows a bi-polar magnet system consisting of two equal horse-shoev shaped halves a,

30 around each of the yokes of which a field-winding b is wound. The shanks of the two horse-shoe shaped halves a which are directed towards each other have the same polarity and surround a tripolar armature c', which is to rotate in a clock- 35 wise direction. The three armature teeth :1 have each in the middle of their periphery a groove e parallel to the axis of the armature. These grooves increase the magnetic resistance of the armature, but in the armature position illustrated, in which the turning moment of the armature of usual construction'is ata minimum, they at the same time alter, (probably in connectionwith an armature reaction) the distribution of the magnetic flux in such a way that in this po- 45 sition the turning moment is increased in a considerable degree and the armature can overcome the unfavourable position. t

Figure 2 also shows a bi-polar magnet system consisting also of two equal horse-shoe shaped halves a and an ordinary tri-polar' armature c. Of the four pole-shoes f of the magnet system, two have each a pointed or tapered extension g at diametrically opposite points in the pole gaps receiving the winding. By these extensions g the turning moment is improved in the unfavourable position of the armature.

The extensions 9 in Figure 2 act like an irregular overlapping of the two field-pole systems. The same action can be obtained if the pole-shoes of 60 the magnet system are somewhat angularly dis April 20, 1931 placed in relation to the yoke, as shown in Fig. 3. In this figure, c is again the usual tri-polar armature. A single horse-shoe shaped frame It is here adopted, about the yoke of which lies'the' exciting winding. The pole-shoes i have pole races of equal extent formed thereon and are so staggered that when one pole of the armature is directly opposite one pole of the field yoke the other pole shoe of the field yoke extends over half the periphery of'one oithe other armature poles. Thus, due to the unsymmetrical disposition of the pole shoes an edge action is obtained, which improves the turning moment.

In Fig. 2 the armature o is assisted by the projections g in starting from and passing through each of its positions of minimum turning moment, since they cause such a distribution of magnetic fiux at the field poles that a turning moment on the armature is produced at the time. Assuming, for example, that the direction of rotation is clockwise from the position of minimum turning moment there shown, then with the lower armature pole d in mid-position, the presence of the extension 9 at the right brings its field pole nearer than it would otherwise be to the leading tip of the upper right armature pole, half of which is embraced by the upper right field pole. This unsymmetrical arrangement of the field and armature poles results in a turning moment on the armature in clockwise direction from the position shown, which would not be the case if the extension 9 were omitted and the field poles arranged symmetrically. Likewise, assuming a clockwise direction of rotation in Fig. 3, the leading tips of the pole shoes 1' result in a similar way in a turning moment on the armature c at each of its mid-positions, one of which is there shown. With the direction of flow of current in the armature and field windings reversed with respect to each other, the same effect occurs in counterclockwise direction of rotation of the armature sisting of toothed wheels and a crank is intro-' duced between the shaft k of the armature c and a shaft 1, which gearing converts the rotary movement of the armature 0 into a reciprocatory movement. The wiper lever, which is not shown, is fastened in known manner on the shaft-l.

I declare that what I claim is:

1. In an electric motor having a tri-polar armature, a horse-shoe type field magnet having two unequally extending limbs and a transverse yoke, the longer of said limbs extending perpendicularly from said yoke, the shorter of said limbs extending at an angle from the perpendicular, and an arcuate pole face or equal size formed upon and extending to the outer end of each said limbs.

2.- In an electric motor having a tri-polar armature, a field magnet having two limbs of unequal length and a transverse yoke, a pole face of equal extent formed upon each of said limbs and extending to the ends thereof, said pole faces being disposed at unequal distances from the ion- -gitudinai center of said transverse yoke, whereby respective chords taken across. each pole face are in non-parallel relation.

GUSTAV ZEININGER. 

